Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Guitar Pro 7 - Create, play and share your tabs
cassini - Polyphonic Synthesizer for iPhone/iPod touch
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
zMors Modular - Full featured modular synthesizer for iOS
OpenMPT - OpenMPT is a popular tracker software for Windows.